Production of vacuums



Patented June 9, 1931 UNITED STATES PATENT OFFICE ALPHONS o. Janene, or MOUNT LEBANO N, AND HERBERT J. WEST, OF GRAFTON,

PENNSYLVANIA, ASS IGNORS TO THE SELDEN COMPANY, OF PITTSBURGH, PENN- SYLVANIA, A CORPORATION OF DELAWARE PRODUCTION OF VACUUMS No Drawing.

This invention relates to methods of producing vacua, and particularly by means 0 high-vacua condensation pumps.

In the past high-vacua had been produced in condensation pumps using mercury as a circulating medium because of its moderately.-

low vapor pressure and its stability. In the ordinary type of vacuum pump, where the vacuum. desired is not as high, oils have ordinarily been used as a sealing medium. Such sealing medium does not require as high a resistance to heat as does the medium use in a condensation pump because the sealing medium in an ordinary type of low vacuum pump is not distilled and condensed. It has been proposed to use certain higlroils in condensation pumps, and while these prodp ucts possess in many cases a vapor pressure even lower than that of mercury, they have not proven successful as they tend gradually to break up on heating and are usually mixtures and do not have a constant vapor pressure at different rates of distilling so that fluctuations in the distilling will result in vapors of 'difierent compositions and correcondensates of different vapor pressures. Despite its high price and great weight therefore mercury has hitherto been practically the only medium used in condensation vacuum pumps.

Accordiri to the present invention hexahydrophtha ides are used as a circulating medium for .high-vacua condensation pumps or as a sealing and lubricating medium for the ordinary types of lower vacuum pumps. The hexahydrophthalides are either liquids or low melting solids which are extremely stable and possess very low vapor ressures. At the same time they are much lig ter than mercury, and volume for volume cost but an insignificant fraction of the cost of mercury. The lighter weight simplifies the construction of the pump, and the much lower cost greatly decreases the investment required in the apparatus.

While the hexahydrophthalides are particularly important in hi h-vaeua pumps of the condensation type, t ey of course may also be used as a sealin medium for low vacuum pumps, and in its broader aspects Application filed March 28, 1931.' Serial No. 526,136.

such devices are included in the present inf vention. It should be understood that in its essence the present invention is directed to the use of the novel sealing medium in Vacuum pumps and is not limited to any particular structural design of either condensation or ordinary vacuum pumps. It is an advantage of the present invention that they are directly applicable in theordinary designs of pumps. Naturally of course in condensation pumps the dimensions of orifices d and the heating means must be suitably adjusted to the physical characteristics of the hexahydrophthalides but no change in design is necessary.

While in the preferred embodiments of the resent invention hexahydrophthalide is used, so that a uniform vapor pressure is most easily achieved, it is possible to mix.these substances with other sealing medium such as esters of keto aromatic acids, esters of phthalic acid and the like, and in its broader aspects the present invention includes the use of any sealing medium which contains a hexahydrophthalide in substantial amounts, Whether or not this is the only component of the medium.

What is claimed as new is:

1. In a method of producing high-vacua by means of condensation pumps the improvement which comprises uslng a pumping substance for providing the propellent vapor, one containing at least one hexahydrophthalide.

-2. In combination a pumping chamber, a

supply of liquid containing at least one which the liquid consists of hexahydroph-'.

thalide itself.

Signed at Pittsburgh, Pennsylvania, this 24th day of March, 1931.

ALPHONS O. JAEGER. HERBERT J. WEST. 

